The use of salts to thicken surfactant systems and enhance viscosity is not new (see Canadian Patent No. 2,211,313). Typically, a so-called peak viscosity is achieved when salt is first added, and further addition of salt leads to viscosity reduction (this is known as oversalting). When the composition is diluted, the “oversalted” composition then increases in viscosity once more in a process referred to as “dilution thickening.”
Dilution thickened compositions typically will form a film on the skin which lacks cohesion. As such the film will dissolve and quickly wash away. As such, the dilution thickening compositions are generally perceived as readily rinsable and difficult to spread.
Unexpectedly, applicants have found that when, in addition to the level of salt required to form “oversalted” compositions, an associative thickener (e.g., hydrophobically modified PEG such as PEG-200 glyceryl tallowate, such as Rewoderm® LIS75 or PEG-7 glyceryl cocoate) is also used, the film on the skin is far more cohesive, thereby leading to reduced rinsability and greater spread on the cleansed surface. This in turn permits consumer to use less product and offers sensory benefit, both with and without use of additional applicator/implement during use.
In addition, applicants have found use of associative thickener lessens the amount of salt needed to induce dilution thickening.
WO 94/16680 to Unilever discloses aqueous dilution thickening, concentrated liquids comprising 20 to 60% surfactant other than soap or primary alcohol sulphate. The compositions are said to form a low viscosity, lamellar phase in the undiluted product and, when diluted, to form into a more viscous rod or hexagonal phase.
There appears to be no disclosure of the hydrophobically modified associative thickeners of the invention or of the effect of such thickeners in lowering level of salt required for dilution thickening.
Canadian Patent No. 2,211,313 also discloses compositions which have been oversalted and increase in viscosity upon dilution.
While there is a broad list of thickeners disclosed (page 9, third paragraph), there is no disclosure of the specific use of hydrophobically modified associative polymer or of its effect in lowering salt level required to see dilution thickening effect.
U.S. Pat. No. 6,427,177 to Williams et al. entitled “A Separating Multiphase Personal Wash Compositions in a Transparent or Translucent Package” discloses a biphasic or multiphasic liquid in which, in one of the phases, can be found high levels of electrolyte and an associate thickener.
The compositions of the reference are multiphasic before dilution and may or may not be monophasic upon dilution. They also require that much higher levels of electrolyte be used in order to form the biphasic in the first place. By contrast, the compositions of the subject invention are single phase compositions prior to dilution.
There is also no disclosure of a process for lowering level of salt required to obtain dilution thickening effect using specific associative thickeners.